Measuring exhaust air after hardening furnaces using rock wool as an example

Exhaust air measurement to increase energy efficiency in laden/hot exhaust gases

Process data

Measuring task:
Flow velocity for process regulation

Measuring point:
Exhaust air of the hardening furnace

Measuring range:
Up to 0.5 .. 10 m/s

Process pressure:
Approx. atmospheric

Process environment:
Up to 240 °C

Recommended products

Vortex Probes VA40 ZG4

ProductProduct data sheet


When manufacturing rock wool or glas wool and similar materials, the mineral wool’s fibres are pressed, binding agents (resins when using rock wool) are added and heated in the hardening furnace. It hardens the binding agent and results in the actual product. The hardening furnace’s exhaust air is laden with these binding angents which can pose a strain on the possible measuring method.

Your advantage

The process is controlled and secured through the measurement; around the clock!
Our vortex sensors are suited for the use up to 240 °C
Our vortex sensors can be used under adverse circumstances

Production of rock wool

Manufacturing mineral wool, especially rock wool is a complex and energy consuming process. Raw materials for rock wool are spar, dolomite, basalt, diabase, anorthosite, and recycled material from the production process. Starting material for mineral wool are up to 70% waste glass, sand, lime stone and soda. It’s all combined to create a liquid mass (coke serves as an energy supplier). This mass is melted and sprayed in liquid form into fibres. Afterwards resin is added as a binding agent to the fibrous base material. The resulting homogenous intermediate product is then sent through the hardening furnace. There the hardening resin combines with the fibres and results in the desired fibre composite material.


This energy consuming manufacturing process is a main focus for the producers due to increased energy costs. In order to counteract the increased energy costs the exhaust air in the existing plants needs to be regulated. These and other energy related measures can be used to meet the requirements for certification.

Exhaust air measurement at hardening furnaces

The hardening furnace’s exhaust air is discharged through filter systems. Depending on the product, different partly high temperatures are reached. The exhaust air is also laden with binding agents (resins) which in the past led to failure of the used measuring technology.  

This is where our vortex sensors come to use. Given frequent cleanings they even work under extreme conditions (see photo below).
They have a very high resistance to soil and condensate. The goal of the use is to only pull so much exhaust air through an exhaust air ventilator from the pipe to complete the hardening process without wasting energy. All while ensuring that no explosive gas mixtures arise. To avoid this, a sufficient amount of exhaust air (amount depending on the product) must be detracted (forced venting). With the measured flow velocity a cover is accordingly regulated.